Can anyone give me tips or refer me to a website on how to make teeth look realistic.

I am painting a portrait for someone and the portrait itself looks extremly realistic except for the teeth.

any suggestions?

I couldn't find anything online to point you to, but can only offer the following tips...

Don't try too hard to make them look too realistic, this will only call attention to the mouth itself and that's not what the portrait should be about. Don't make them too white...and don't put too much emphasis on defining the spaces between them or painting them individually - stay away from any hard lines on the teeth or gums...softening the lines is key to keep the focus away from the mouth. Keep from painting the gums too pink or all one tone

When drawing or painting teeth suggest them rather than put them all in individually and don't forget that the teeth go round the oval shape of the head so there is shadow at each corner of the mouth.

I also found these insructions for painting a realistic looking sculpture. It's for a vampire but oh well, lists some colors you might use:

For the mouth, I paint the inside dark brown using Burnt Umber, and fade the color to a reddish shade as it gets to the outer edge by adding Red Oxide and a touch of White to the mix. I darken the lips with washes of Burnt Umber, Red Oxide and Payne's Gray. Using the Red Oxide/White color I paint the Vampire's gums. I then basecoat his teeth with the same color I used to basecoat the eyes. Next, I highlight the tips of the teeth by adding white to the basecoat color. After the teeth have dried, I add washes of Raw Siena to make them more ivory in color, and a Burnt Umber wash to darken them along the gum line.

Hope these help some. And I agree with Lydia's comment about not painting individual teeth. They'll end up looking like a white picket fence.